I intend to study the regulated expression of the rrn operons which specify the ribosomal RNAs and certain transfer RNAs in E. coli. My approach will be the analysis of three distinct mutant strains -rpoD800, NS1 and S8 - all of which are preferentially thermolabile for stable RNA synthesis. The defective proteins in the first two strains have been identified as the sigma subunit of RNA polymerase and the groE protein, respectively: the temperature sensitive gene product has not yet been identified in the S8 strain. I propose to identify and examine the protein-protein and protein-nucleic acid interactions that govern the inhibition of the synthesis of the stable RNAs in the mutants. My experiments focus on determining: 1) if the thermolabile event affects the initiation of elongation of rRNA chains; 2) whether the in vivo inhibition phenomenon can be duplicated in vitro; 3) whether altering the physiological environment of the cell affects the temperature sensitive response; 4) the identity of the thermolabile protein in the S8 strain; and 5) if more mutations specifically affecting stable RNA synthesis can be found at other genetic loci. Some studies will entail the use of the recently determined restriction endonuclease maps and sequencing studies which have established the existence of tandem promoters for the E. coli rrn operons. I would like to ultimately prove or disprove whether there are proteins in addition to RNA polymerase which act as positive regulators of rRNA biosynthesis in E. coli.